The present invention relates to a concentrated winding stator coil for an electric rotary machine.
A concentrated winding stator, conventionally proposed in the field of electric rotary machines, includes a plurality of phase windings each consisting of same phase coils connected with each other and wound in a concentrated manner around respective teeth of a stator core (hereinafter, referred to as tooth coils). From requirements of the winding work, this kind of concentrated winding stator is generally used for an assembled core which is formed by assembling separated partial cores of respective teeth into a stator core.
The tooth coils of a concentrated winding stator are wound around the teeth to have a required turn number. Two neighboring turns are usually disposed to be adjacent to each other in the axial direction on a circumferential surface of the tooth. The winding order for this concentrated winding stator is as follows.
First, the winding operation starts from one radial end side of a tooth to the other radial end side of this tooth to arrange a first layer coil. Then, turning the advancing direction, the winding operation restarts from the other radial end side of the tooth to the one radial end side of this tooth. Thus, a second layer coil is arranged on the first layer coil. Similarly, a third layer coil is arranged on the second layer coil so as to realize a highly densified winding. The first layer coil, the second layer coil, and the third layer coil are collectively referred to as “layer coils”, in the following description.
The Japanese patent application Laid-open No. 2002-112484 (hereinafter referred to as prior art 1) proposes, in order to improve a slot space factor, to alternately dispose tooth coils wound around teeth each having a trapezoidal cross section in the radial direction and tooth coils wound around teeth each having a rectangular cross section in the radial direction, based on the fact that the circumferential width of each tooth is constant and a slot is widened in the radial direction from its inside to the outside (refer to FIG. 9). The Japanese patent application Laid-open No. 2001-186703 (hereinafter referred to as prior art 2) discloses, as a tooth coil winding arrangement for a concentrated winding stator, a tooth coil with a starting end disposed at a proximal end portion (or distal end portion) of a tooth and a terminal end disposed at a distal end portion (or proximal end portion) of the tooth. Furthermore, this prior art document discloses, as another tooth coil winding arrangement, a tooth coil with starting and terminal ends being both disposed at the distal end portion of a tooth.
However, the tooth coils disclosed in the prior art 1 are complicated to manufacture. As the trapezoidal tooth coils have a large circumferential width, the axial length of a stator inevitably increases by an amount corresponding to the axial length of this trapezoidal tooth coils.
On the other hand, the tooth coils disclosed in the above-described prior art 2 have the following problems. First, in the process of arranging a phase winding by connecting tooth coils of the same phase via crossovers in serial or parallel to each other, at least one end of each tooth coil is positioned at the distal end portion of the tooth. In the case of using short crossovers, the crossovers or lead wires extending from end portions of the tooth coils and connected to the crossovers will be positioned very closely to the circumferential surface of a rotor. If these wires are loosened and subjected to vibrations, there will be the possibility that the wires contact with the rotor or installation work for the rotor will become complicated. Furthermore, the connection by means of a crossover between one end of a tooth coil existing at the distal end portion of a tooth and one end of other tooth coil needs to be performed at the outside of an end face of the tooth in the axial direction. Thus, the axial length of the concentrated winding stator increases. Furthermore, the crossover needs to be disposed on the tooth coil wound around the tooth. Accordingly, the axial length of the stator further increases.